BoilerFaultCodesTechnical description
If the overheat Safety Temperature Limiter operates as indicated by illuminated reset light, open the controls cover and turn temperature control to “0” (anticlockwise) and then back to original position
What causes this fault?
This fault occurs when the water inside the boiler exceeds a safe temperature limit, triggering a safety shut-off to protect the internal components. The most common reasons are a failing circulation pump that isn't moving water through the system fast enough or a buildup of debris that has partially blocked the heat exchanger.
This issue often surfaces during the first cold spell of autumn when the heating is turned back on after being idle all summer, which can cause internal parts like the pump to seize.
Engineer required
This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.